Filament tensioning and supporting arrangements for electron tubes



D86. 20, P. HAAS FILAMENT TENSIONING AND SUPPORTING ARRANGEMENTS FOR ELECTRON TUBES Filed May 6, 1942 INVENTOR ATTORN United States Patent FlLAlVIENT TENSIONING AND SUPPORTING ARRANGEMENTS FOR ELECTRON TUBES Paul Haas, Emporium, Pa., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application May 6, 1942, Serial No. 441,886

16 Claims. (Cl. 313278) This invention relates to electron discharge devices and in particular to discharge tubes with filamentary thermionic cathode.

When the filament in these tubes is heated to the temperature needed for thermionic emission, the filament expands and tends to sag. In order to prevent sagging of the filament, which might cause short circuits between the elements or a variation of the tube characteristics, it is necessary to provide means to keep the filament under a tension.

This tension usually is provided by a spring connected to one end of the filament, the other end of the filament being rigidly fixed to one or more supports determined by the shape of the filament. In the case of the so-called hair-pin filaments, the two lower ends of the hair-pin may be welded to the lead-in conductors which supply the heating current while the upper part of the hair-pin filament forms a loop or bight which is coupled to a hook attached to a tension spring. Single strand filaments are usually welded at one end to one of the heater current supply leads, and at the other end to the tension spring, which may form part of the other heater current supply lead.

Two types of tension spring are commonly used in these tubes. The first type, which is ordinarily used with single strand filaments and hair-pin filaments of small diameter, consists of a slightly bent or bowed piece of spring wire attached at one end to the filament perpendicular to the main extensional plane of the filament. The other end of the spring is fixed to a support, usually a rod parallel to the tube axis. Such a spring acts substantially as a cantilever, and has the advantages of simplicity and low cost. It has, however, very little rigidity in a direction perpendicular to itself and to the filament. The adjustment of its tension is at the discretion of the mounting operator and its tension depends, therefore, on the personal element. In large scale production this results in undesirable variations of filament tension from tube to tube and in a comparatively large number of filament burnouts because of excessive tension, or of short circuits because of insuflicient tension. A further variation of the tension inherent in this type of spring support is caused by the welding of the spring wire to the support, which often results in an erratic change of the elastic properties of the spring.

A second type of filament spring is ordinarily used in larger tubes for hair-pin filaments. This type consists of a helical compression spring formed by winding around a cylindrical or conical mandrel. The lower end of the helix is supported by an insulator above the upper end of the filament and the uppermost helix turn is connected to a piece of bent-back wire which returns downwardly through the inside of the helix and through a hole in the support, and usually terminates in a little hook which engages the upper loop end or bight of the filament hairpin. This second type of spring has the advantage that its tension may be exactly adjusted, and that it centers the upper end of the filament with respect to the other 2,728,017 Patented Dec. 20, 1955 tube elements in a simple way. The nature of this suspension spring is, however, restricted to larger size tubes and to the hair-pin type of filament.

The filament spring according to the invention avoids the disadvantages of the two known types and it may be used in connection with any desired filament type or size.

It is a principal object of the invention to provide a filament tension spring of great mechanical rigidity which may be easily adjusted to a desired tension.

Another object of the invention is to provide a filament tension spring whose tension can be easily reproduced uniformly from tube to tube in large scale production.

According to another object of the invention, means are provided which insure transverse rigidity of the spring by means of a symmetrical arrangement of two parts.

It is another principal object of the invention to provide an electron discharge tube of very small dimensions including a filamentary cathode, which does not change its characteristics when exposed to unusually high mechanical shock and which maintains substantially constant filament tension for the whole range of filament temperatures from room temperature and lower up to the temperature of normal operation and higher.

Another feature of the invention relates to the method of winding two cooperating symmetrical parts of the spring from a single piece of wire.

According to one feature of the invention, means are provided which insure equal elastic characteristics of the two parts of the spring.

Another feature relates to an elastic filament suspension whose tension is primarily dependent upon the cooperation of two torsional spring members.

Another feature of the invention relates to a pair of helical spring members whose common axis is perpendicular to the main extensional dimension of the filament.

A further feature relates to the method of mounting a filament into an electron discharge tube.

The invention in its several embodiments will now be described in connection with the drawing, in which,

Fig. l is an elevational view, partly sectional, of an electron tube embodying the invention.

Figs. 2 and 3 are twodifferent views of the new filament spring ready for mounting.

Figs. 4 and 5 are two dififerent views of a modified filament spring.

Fig. 6 is an enlarged perspective view of the filament and spring tension arrangement of Fig. 1.

Fig. 7 is a top-plan view of part of Fig. 1.

Referring to Figs. 1 and 6, 1 represents a tube header such for example as disclosed in Patent No. 2,250,184 into which are sealed in a vacuum-tight manner the supports 2 and 3. The supports 2 and 3 extend below the header and may be used for applying external heater voltage to the filament. In the particular tube shown, the members 2 and 3 also act as plug-in prongs.

One end of filament 4 is welded to tab 5, the other end being welded to tab 6 which in turn is welded to filament spring 7 at point 8. The two helical parts 9 and 10 are threaded over a horizontal support 11 which is welded at 12 to support 2. A second horizontal support 13 is welded to support 2 at point 14 and ends 15 and 16 of the tension spring are welded to support 13 at points 17 and 18.

Figs. 2 and 3 show the shape of the preferred form of spring before it is slipped over horizontal support 11. It is wound over a mandrel that carries a little pin extending radially therefrom at its center. The pin has a notch at a distance from the mandrel corresponding to the length L in Fig. 2. The apex 19 of a V-shaped piece of spring wire is inserted into the notch and the mandrel is then turned so as to produce the two symmetrical coils 9 and 10 from the center outward, while the open end of the V-shaped wire is held under tension. The winding is stopped when the desired number of turns has been wound, apex 19 is released from the pin, the pin pulled out of the mandrel. and the spring slipped off the mandrel.

Preferably, the winding operation is continued long: enough so the legs 20, 21,- 22 and 23, Fig. 2-, are located inone plane. when thespringis free of tension.

The filament 4 provided with tabs 5: and 6, is then;

weldedto point 19 of the spring. The spring coil is then slipped over horizontalsupport 11, the filament-isslipped through the mount. and welded tov support 3 at its lower end. The legs 20' and- 21 are kept in'horizontal position as.represented by the-dotted lines (Fig. 6.) when the filament. is, straight, and a. position of support. 11 with respecttoi vertical support. 2 is found for which thesetwo conditions; are fulfilled. In this way point 12 is located and; the: two supports are welded together at 12'. At a lastoperation, the. legs 20. and 21 are bent down topoints 17;- and"- 18 of second horizontal support 13, into the position, ShOWlI.i11 Fig. 6: and welded to. this support at said points1=7 and 18.

Thertension of the filament is fixed by the angle 15"- 22-15 which is about 90 in Fig. 6. The tension can thusbe. easily reproduced and kept uniform for all tubes mounted in this way. It is obviousthat the correct value of the tension can easily be obtained by the proper choice of the wire. thickness, the length L and the number of turns wound in the sections 9 and 10. In thiszway it is possible to combine large mechanical ruggedness with any: desired degree of stiffness of the spring. The filament tension decreases with increasing length L, increasing'num ber of turns in sections 9 and and decreasing'wire diameter; The wire diameter determines substantially the sensitivity of the spring against shock and the length L may be accommodated to the given space requirements.

Once the dimensions are fixed, the filament tension depends only on the torsion of the coils 9- and 10, i. e., on the angle -22-15- by which arm 20 is bent for the final welding operation, but is independent of the elastic.

characteristics of the wire at the ends 15 and 16 which are welded" to the support 13.

A particular advantage of the suspension as described consists in the transverse rigidity of the legs 22 and 23 in their own plane, due to the angle formed by this part of the spring; The preferred position of this plane is perpendicular to the filament, butthe exact position is: not too-critical;

While. for the purposesof simplicity in explanatiomthe mount of Fig. 6 shows. only the filamentary cathode, it will be understood that any well-known electrode arrangement. may be employed; Thus, there is shown in Fig; 1,, a' complete radio tube embodying the filament support and tensioning arrangement of Fig. 6. In Fig. 1', the parts corresponding to those ofFig, 6 bear thev sam'e designation numerals. The bulb 25 is closed off atits lower endby a glass header (not shown). corresponding to header 1 and through which are sealed the various plug-in and lead-in pins. 26. For a detailed description of" this type of" header, reference may be had to Patent No; 2,250,184. The uprights 2' and 26 carry a pair of mica discs 27, 28', between which are assembled the heli callywound' control grid 29 and tubular metal plate 30. The discs 27"and' 23' are. provided centrally thereof with respective openings 31 through which pass the tensioned fil'ament 4i Preferably, although not necessarily, the. openings 31 are triangular and the filament is t'ensioned so that it bears adjacent an end; lightly against the corner of'th-e' associated triangular opening. If desired, the tri angular openings in the two discs 27 and 28 may be arranged so that the filament at its upper end engages a different corner of' the. triangular opening in the disc 27, fno'm the corner in' the lower disc 28that' is engaged by the lower end of the filament. In other words, the engagementof the" filament with the respective discs 27. and 28 eifects-a' damping in substantially mutually perpendic- 4 ular. planes. For. a. detailed description. of. this. method. of damping, reference may be had to application Serial No. 426,696, filed January 14, 1942, Patent No. 2,303,278, November 24, 1942.

Various changes and modifications may be made in the disclosed embodiments without departing from the spirit and scope of the invention.

What I claim is:

l. A tensioning arrangement for heatable filaments, comprising a rigid support extending transversely to the. filament but spaced laterally therefrom, aspring wire having first and second linear portions joined by an intermediate looped portion, said linear portions being normally substantially in the said plane, said looped portion surrounding said support but without being fastened thereto, means to fasten the first of said linear portions to said filament, and means to fasten the second of said linear portions and to hold it in a d'eflectedposition whereby the-first linear portion tends to turn around said support as a pivot to exert the desired tension on saidfilament.

2. A spring tensioning arrangement for heatable filaments, comprising a rigid supportextending substantially parallel to-thefilament, a second support fastened to the first support and extending transversely to the filament, aspring Wire having a v shaped' section terminating in linear end sections with a coiled section between each leg of the. V" section and each of said end sections, said other support extending throughboth said coiled sections and with the apex of the V section fastened to-the filament, said linear sections being deflected out of the plane of the V section and anchored in deflected' position.

3'. A spring tensioning arrangementaccording to claim 2 in which a third support is fastened to the said rigid support and issubstantially parallel to said second support, the ends of said linear sections being fastened to; said third support.

4. A- spring tensioning arrangement for heatable filaments, comprising a rigid upright extending along the filament but laterally spaced therefrom, a pair'of parallel spaced arms. fastened to-said' upright, a spring wirehaving a- V'-shap'ed= section with the apex of the V fastened to one end of the filament; said spring wire having substantially linear end portions connected to' the legs ofi the V through respective coiled sections, said coiled sections surrounding one of said arms" and beinglocated symmetrically with respect to said filament; said linear sections being fastened tosaid other arm.

5. A spring tensioning' arrangement according to claim 4' in which said coiled sections-surround said one of saidarms so that when said linear endsections aredeflected downwardly out of the plane of" the V-shaped section; they tend to cause rotation of said v shaped sectionaround said arm as a pivot.

62 A non microphonie filament supporting arrangement for electron tubes and the like comprising a pair of spaced insulator members having aligned openings, at

filamentpassingthrough said openings, means to anchor the lower end of the filament beneath one of said insulator members, and means to anchor theupper end of the filament above the other of said: insulatorme'mbers while exerting a desired tension on said filament, the last-mentioned means comprising an upright extending netween said insulator members laterally spaced from' the filament, a' transverse arm adjacent the upper end of'said upright, a spring member having" a V-shaped section and a pairofsubstantiallylinear end sections withintervening coiled sections, said coiled sections being supported on and surrounding said transverse arm but without being. fastened" thereto, means to. anchor the apex of the V-shaped section to the upper end of the filament and means to, deflect and hold said linear. end. sec.- tions at an angle to. the V-shaped' section whereby said v shaped section tends to rotate around said transverse arm but is resiliently restrained against rotation by the tension of the filament.

7. A non-microphonic filament supporting arrangement according to claim 6 in which said insulator members are in the form of discs having triangular openings and said spring arrangement maintains said filament in bearing contact with an edge of each opening.

8. In a rugged tube having an envelope and a filament in the envelope, a filament support comprising a bar mounted in the envelope, a pair of spring coils on the bar, means for anchoring one end of each coil, lever arms on the opposite ends of the coils and converging from the coils to a bight, and means for connecting the bight of said arms to one end of the filament.

9. In a rugged tube having an electrode assembly including a filament, tensioning means for supporting the filament in the electrode assembly and comprising a spring having a generally V-shaped section terminating in coil sections, said coil sections terminating in substantially linear end sections.

10. An electron tube having an envelope and a filament in the envelope, a filament support comprising a bar mounted in the envelope, a pair of spring coils disposed in endwise alignment on the bar, and means anchoring one end of each coil, the other ends of said coils extending to a bight, said bight and said filament being connected together and said coils being biased to tension the filament.

11. An electron tube including an envelope, a filament enclosed therein, a filament tensioning spring in said envelope and having a central V-shaped section connected to tension said filament, said V-shaped section terminating in substantially linear end sections with respective intervening coiled sections extending outwardly from the legs of the V-shaped section and having a common axis, said linear end sections extending substantially transverse to said axis, and means anchoring said linear end sections and supporting said coiled sections.

12. An electron tube having an envelope enclosing a filament, a filament tensioning spring in said envelope and having a central section connected to tension said filament, coiled sections extending from said central section outwardly along an axis, the opposite extremities of said coiled sections being anchored, and a fixed bar extending through said coiled sections and providing support therefor.

13. A filament tensioning spring having a V-shaped section terminating in substantially linear end sections with respective intervening coil sections, said coil sections extending outwardly from the legs of said V-shaped section along a common coil axis, and said linear sections and said V-shaped section extending substantially transverse to said axis and lying in the plane of said axis in an unstressed condition.

14. A filament tensioning spring having a V-shaped section terminating in substantially linear end sections with respective intervening coil sections, said coil sections extending inwardly from the legs of said V-shaped section along a common coil axis, and said linear sections and said V-shaped section extending substantially transverse to said axis and lying in the plane of said axis in an unstressed condition.

15. A filament tensioning spring having a V-shaped section terminating in substantially linear end sections with respective intervening coil sections, said coil sections extending outwardly from the legs of said V-shaped section along a common coil axis, and said linear sections and said V-shaped section lying in the plane of said axis in an unstressed condition, said V-shaped section extending laterally of said axis in said plane and in an opposing direction to said linear end sections.

16. A filament tensioning spring having a V-shaped section terminating in substantially linear end sections with respective intervening coil sections, said coil sections extending inwardly from the legs of said V-shaped section along a common coil axis, and said linear sections and said V-shaped section lying in the plane of said axis in an unstressed condition, said V-shaped section extending laterally of said axis in said plane and in an opposing direction to said linear end sections.

References Cited in the file of this patent UNITED STATES PATENTS 1,566,292 Vander Bijl Dec. 22, 1925 1,675,073 Weeks et al June 26, 1928 1,980,936 Van Steenis Nov. 13, 1934 2,146,361 Stilson Feb. 7, 1939 2,259,703 Miller Oct. 21, 1941 2,438,377 Stilson Mar. 23, 1948 

